There is considerable interest in processes for the preparation of semiconductor nanocrystals, the applications for which include, for example, optical communications, photonic chips, photovoltaic devices, and biolabels for bioimaging. Traditional preparative routes to III-V semiconductor nanocrystals require the use of coordination solvents such as trioctylphosphine oxide (“TOPO”) or dodecylamine (“DA”) and generally require long reaction times at high temperatures (i.e., 3–6 days at ˜300–400° C.). See, for example, U.S. Pat. No. 6,306,736 to Alivisatos et al. Decomposition products resulting from these methods have been shown to possess optical properties which have the potential to interfere with the optical properties of the desired III-V nanocrystals. Moreover, the III-V semiconductor nanocrystals prepared by these methods are generally polydispersed (1–20 nm) and the results are somewhat erratic or irreproducible. An added disadvantage is that when any of the commonly utilized surfactants are exposed to high temperatures (>100° C.), their optical properties also have the potential to mask or obscure the optical properties of the desired nanocrystals.
Other existing preparation technologies include Molecular Beam Epitaxi (MBE) and Chemical Vapor Deposition (CVD). However, although both of these methods are excellent techniques for the preparation of thin film or bulk III-V semiconductor materials, neither technique is capable of producing monodispersed III-V semiconductor nanocrystals and neither offers control or exchange of the surface capping material which would allow incorporation of the semiconductor nanocrystals into desired host matrices.
Compounds of the type M(ERx)3 (M=Group III metal; E=Group V or Group VI element; R=organic group; x=1 if E is Group VI element, and x=2 if E is Group V element) may be used as precursors for the synthesis of III-V semiconductor nanocrystals. The best precursors should be soluble in non-coordinating organic solvents, that have high boiling and high decomposition temperatures, and which can be prepared in very high purity. The typical synthetic routes to these types of compounds are either hydrocarbon elimination reactions (Equation 1) or metathesis reactions (Equation 2).

The major source of impurities in precursors prepared by the elimination reactions originates with the high temperatures needed to initiate the elimination reaction between the pure starting materials, the organo group III compound, and the Group V compound. Elimination reactions for gallium-nitrogen systems require 100–130° C., whereas gallium-phosphorus compounds need 110–150° C. For example, the compounds [Me2GaNH2]3, [Me2GaN(H)(Me)]3, [Me2GaNMe2], [Me2GaN(H)(t-Bu)]2, and [Me2GaNPh2]2 were prepared from the neat reagents, GaMe3, and the corresponding amine, at 90, 125, 125, 110, and 120° C., respectively (Coates, J. Chem. Soc. 1951 (2003); Park et al., Organometallics 11:3320 (1992); and Coates et al., J. Chem. Soc. 233 (1963)), whereas [Me2GaN(H)Ph]2, [Me2GaN(H)Ad]2 (Ad=1-adamantyl), and [Me2GaN(H)Dipp]2 (Dipp=2,6-i-Pr2C6H3) were formed from GaMe3 and the corresponding amine in refluxing toluene (bp 110° C.). Waggoner et al. J. Am. Chem. Soc. 113:3385 (1991). The diethylgallium-nitrogen, diethylgallium-thiol and diethylgallium-phosphorus compounds [Et2GaS(SiPh3)]2, [Et2GaPEt2]2 and [Et2GaN(C2H4)]2 have been prepared directly from GaEt3 and HS(SiPh3), HPEt2 and HN(C2H4), respectively, neat at 70, 100–150 and 110–150° C., respectively. Beachley et al., Organometallics 15:3653–3658 (1996); Maury et al. J. Phys (Paris) 43:C1–347 (1982); Maury et al., Polyhedron 3:581 (1984); and Storr et al., J. Chem. Soc. A 3850 (1971). The gallium-phosphorus compounds, [Me2GaPMe2]3, [Me2GaPEt2]2, and [Me2GaPPh2]2, required heating the corresponding neat reagents to 150, 160 and 110° C., respectively. Beachley et al., J. Chem. Soc. A 2605 (1968) and Coates, J. Chem. Soc. 1951 (2003). It is noteworthy that when GaMe3 and H2NMes (Mes=2,4,6-MeC6H2) were combined in refluxing toluene and then heated at 190° C., products indicative of orthometalation reaction were observed. Waggoner et al. J. Am. Chem. Soc. 113:3385 (1991). Metathesis reactions on the other hand, require more reagents with multistep synthesis and typically require the use of ether solvents. Since each new reagent or solvent introduces the possibility of impurities, the simplest reaction should give the purest product.
The reaction between Me2Ga(C5H5) and a primary and/or secondary amine or a phosphine (Equation 3) occurs at or below room temperature and provides a convenient, low-temperature route to gallium-nitrogen and gallium-phosphorus compounds of high purity. Beachley et al., Organometallics 12:1976–1980 (1993).Me2Ga(C5H5)+HERR′→1/n[Me2GaERR′]n+C5H6  (Equation 3)
The compounds [Me2GaNH2]3, [Me2GaN(H)(Me)]3, [Me2GaN(H)(t-Bu)]2, [Me2GaN(H)(C6H11)]2, [Me2GaNEt2]2, [Me2GaN(Me)(C6H11]2, [Me2GaN(Me)(Ph)]2, [Me2GaN(Et)(Ph)]2, [Me2GaP(C6H11)2]2, [Me2GaP(Me)(Ph)]3, and [Me2GaPPh2]2 were all prepared at room temperature or below, displaying the ease of cyclopentadiene elimination over methane elimination in gallium organometallic complexes. Beachley et al., Organometallics 12:1976–1980 (1993). The reactions of Et2Ga(C5H5) with HNEt2, HN(H)Me, HN(H)(t-Bu), HP(i-Pr)2, HP(t-Bu)2 and HS(SiPh3) in benzene or pentane provide convenient room temperature routes to the preparation of [Et2GaNEt2]2, [Et2GaN(H)Me]2, [Et2GaN(H)(t-Bu)]2, [Et2GaP(i-Pr)2]2, [Et2GaP(t-Bu)2]2, and [Et2GaS(SiPh3)]2 through cyclopentadiene elimination over ethane elimination. Beachley et al., Organometallics 15:3653–3658 (1996). The compound [(Me3CCH2)2GaPEt2]2 was prepared readily at room temperature by combining Ga(CH2CMe3)3, Ga(C5H5)3, and HPEt2 in a 2:1:3 mol ratio, respectively, in pentane. Beachley et al., Organometallics 16:3267–3272 (1997). This displays the ease of elimination of cyclopentadiene over neopentane, as upon dissolution of Ga(CH2CMe3)3, Ga(C5H5)3 in a 2:1 ratio, the major species present in solution due to ligand redistribution is (Me3CCH2)2Ga(C5H5) which reacts, in turn, with HPEt2 to form the resultant product with no side products or bye-products that would come from neopentane elimination. Thus, for organometallic gallium complexes, cyclopentadiene elimination occurs in preference to methane, ethane and neopentane elimination pathways.
It has recently been discovered that similar cyclopentadiene reactions occurred readily with indium complexes (Equation 4).R2In(C5H5)+HER′R″→1/n[R2InER′R″]n+C5H6  (Equation 4)
The compounds with the simplest formula Me2InO(t-Bu), Me2In(acac) (acac=acetylacetonate), Me2InPPh2, Me2InS(SiPh3), (Me3CCH2)2InO(t-Bu), (Me3CCH2)2In(acac), (Me3CCH2)2InPPh2, (Me3CCH2)2InS(SiPh3), and (C5H5)2InO(t-Bu) were prepared at room temperature or below through cyclopentadiene elimination. Beachley et al., Organometallics 22:1690–1695 (2003) and Beachley et al., Organometallics 22:3991–4000 (2003). Neither methane nor neopentane elimination reactions were observed, and this chemistry demonstrates that cyclopentadiene elimination occurs readily for organoindium complexes.
Traditional preparative routes to II-VI semiconductor nanocrystals require the use of either a coordinating solvent (phosphorus, nitrogen or oxygen based) or a surfactant (phosphorus, nitrogen or oxygen based) and/or a mixture of coordinating solvent and surfactant. See, for example, U.S. Pat. No. 6,225,198 to Alivisatos et al. Also, these traditional preparative routes generally require long reaction times at high temperatures with most of these approaches utilizing very dangerous and reactive metal precursors (i.e., CdMe2 and ZnEt2). Traditional methods of preparing shell materials also require the utilization of coordinating solvents (such as those solvents listed above) and the preparation of elaborate mixtures of metal precursors.
Moreover, current technologies for III-V semiconductor nanocrystals synthesis are dedicated strictly to using commercially available precursors. The most common precursors are the MIII(halides)3. When utilizing these precursors, the resultant semiconductor nanocrystals have the propensity to have halide impurities. These impurities hinder the desired electronic or optical properties of the nanocrystals.
The present invention is directed at overcoming these and other deficiencies in the art.